The veterinary studies area conducts epidemiologic investigations using data compiled by North American veterinary university teaching facilities, the Armed Forces Institute of Pathology (AFIP), the Department of Defense Military Working Dog Agency, NCI's Registry of Experimental Cancers, and other sources when available. These investigations evaluate the role genetic and environmental factors have in the etiology of cancer in animals, and in particular to identify situations where the companion domestic animal may serve as a sentinel for human exposures to environ- mental carcinogens. Major areas of interest are necropsy findings among military working dogs who served in Vietnam; also household and lawn chemical exposures of pet dogs diagnosed with malignant lymphoma or bladder cancer, and record linkage studies of West Virginia military veterans who served in Vietnam or elsewhere during the period of the Vietnam conflict. A study of prostatic disease among military working dogs finds a significant twofold excess of benign prostatic hyperplasia among those with Vietnam service. Further examination of necropsy findings indicates Vietnam veteran military dogs have a fivefold significant excess of prostatic carcinoma compared with military dogs that served elsewhere. Another examination of the necropsy records shows a significant excess of cysts involving the congenital remnants of the branchial apparatus among Vietnam service military working dogs; similar excess, though not significant, is seen among West Virginians who served in Vietnam. A case-control study of 85 pet dogs with cancer of the lower urinary tract found significant associations with owner use of lawn insecticides and professional lawn care application of insecticides, and professional grooming plus exposure to flea and tick dips.